Air-Friendly Gases: What Doesn't Pollute Our Air?

Air is a mixture of gases, most of which are naturally occurring. However, human activities have introduced a significant amount of pollutants to the air, which can have detrimental effects on human health and the environment. These pollutants include nitrogen oxide, volatile organic compounds, carbon dioxide, sulphur oxide, dioxins, and furans. Natural sources of air pollution, such as wildfires, dust storms, and volcanic eruptions, also contribute to the problem. While some gases are more harmful than others, it is important to recognize that even naturally occurring gases can become pollutants when present in excessive concentrations or for extended durations.

Nitrogen is an inert gas that makes up 78% of the air we breathe

Nitrogen is an inert gas, comprising 78% of the air we breathe. It is the most abundant naturally occurring gas in the atmosphere, with oxygen (21%) being the second most common. The remaining 1% of the air we breathe is made up of other gases, primarily argon (0.9%), and trace amounts of carbon dioxide, methane, hydrogen, helium, and others.

Nitrogen is inert, meaning it does not react with other chemicals in the same way that oxygen does. Atmospheric nitrogen does almost nothing, but nitrogen elsewhere on Earth is essential for life. It enters soil and water through the nitrogen cycle, binding with other elements and becoming usable by living things.

The nitrogen we breathe in is mostly exhaled back out, with a small amount being absorbed into the blood. This is because a compound in our blood, called haemoglobin, reacts with the oxygen we breathe in, but not with nitrogen. At high pressures, nitrogen becomes more soluble and can bind to haemoglobin, which is why scuba divers breathe helium instead of nitrogen, to avoid nitrogen narcosis.

Nitrogen is not considered a pollutant, unlike nitrogen dioxide, which is a common air pollutant. Nitrogen dioxide is a result of human activity, such as burning fossil fuels, and is a concern in urban areas.

Carbon dioxide is a greenhouse gas that is harmful in large quantities

Carbon dioxide (CO2) is a greenhouse gas, which means it absorbs and radiates heat. Unlike oxygen or nitrogen, which constitute the majority of our atmosphere, greenhouse gases absorb heat from the Earth's surface and re-release it in all directions, including back toward the Earth's surface. This is known as the greenhouse effect, which is vital for keeping the Earth's climate habitable for humans and millions of other species. Without carbon dioxide, the Earth's natural greenhouse effect would be too weak to maintain a global surface temperature above freezing.

However, human activities have significantly increased the amount of carbon dioxide in the atmosphere, causing global temperatures to rise. Each year, human activities release more carbon dioxide into the atmosphere than natural processes can remove. The primary sources of carbon dioxide emissions are the burning of organic materials such as coal, oil, gas, wood, and solid waste. Other sources include chemical reactions, such as those that occur during cement production.

The annual rate of increase in atmospheric carbon dioxide over the past 60 years is about 100 times faster than previous natural increases, such as those that occurred at the end of the last ice age. Atmospheric carbon dioxide levels are now 50% higher than they were before the Industrial Revolution. In 2023, the global average carbon dioxide concentration set a new record high of 419.3 parts per million, and this number continues to rise each month.

The increase in carbon dioxide and other greenhouse gases is causing climate change, which encompasses rising average temperatures (global warming), extreme weather events, shifting wildlife populations and habitats, rising sea levels, and other impacts. Carbon dioxide is particularly harmful due to its long atmospheric lifetime, lingering in the atmosphere for thousands of years.

While carbon dioxide is essential for the Earth's natural greenhouse effect, its excessive concentration in the atmosphere due to human activities is causing significant harm. The effects of elevated carbon dioxide levels are already being felt, and the planet's climate and ecosystems are at risk of further drastic changes if emissions are not curbed.

Natural gas is a cleaner alternative to coal and petroleum

Natural gas is often touted as a cleaner alternative to coal and petroleum. This claim is based on the fact that burning natural gas produces fewer conventional air pollutants, such as sulfur dioxide and particulates, compared to burning coal or petroleum products. It also generates less carbon dioxide per unit of energy, contributing to improved climate outcomes.

However, it is important to acknowledge that natural gas is primarily composed of methane, a potent greenhouse gas. Recent studies have revealed significant methane leaks from natural gas facilities worldwide, raising concerns about its environmental impact. While natural gas may have cleaner-burning properties, the challenge of mitigating methane emissions during its extraction, transportation, and use remains.

In the context of transitioning away from coal and oil, natural gas can serve as a bridge fuel. Several countries have already adopted natural gas as the preferred fuel for electricity production, benefiting climate change mitigation and air quality improvement. Nevertheless, the transition away from coal and other fossil fuels must be swift to avoid the worst consequences of climate change.

Compared to coal, natural gas extraction and combustion generally result in less environmental harm. Coal mining techniques, such as mountaintop removal, lead to deforestation, habitat destruction, and water pollution. Coal combustion also releases hazardous chemicals, requiring additional treatment processes to mitigate water pollution.

Additionally, emissions from coal and oil combustion can cause acid rain, formed through the reaction of sulfur dioxide and nitrogen oxides with hydroxyl radicals in the environment. Acid rain has detrimental effects on aquatic ecosystems and drinking water supplies. Therefore, natural gas is considered a cleaner alternative in terms of reduced air and water pollution compared to coal and petroleum.

Human-made chemicals like nitrogen dioxide and sulfur dioxide are air pollutants

Human activities such as burning fossil fuels for transportation, electricity, and industry are the primary sources of air pollution. Among the many human-made chemicals that pollute the air, nitrogen dioxide (NO2) and sulfur dioxide (SO2) are two significant ones.

Nitrogen dioxide is a reddish-brown gas that is soluble in water and a strong oxidant. It is formed by high-temperature combustion of fuels used for heating, transportation, industry, and power generation. Vehicle exhaust is the largest source of nitrogen dioxide, but it is also produced by factories, power plants, and natural processes like lightning strikes and the decomposition of organic matter. Exposure to nitrogen dioxide can irritate airways and aggravate respiratory diseases. It is an important precursor to ozone, a pollutant closely linked to asthma and other respiratory conditions.

Sulfur dioxide is produced by power plants and industries that burn fossil fuels containing sulfur, such as coal and oil. It is also generated by the phosphate industry during the production of sulfuric acid. Sulfur dioxide is irritating to the lungs and can lead to a higher incidence of respiratory disease. Additionally, when sulfur dioxide and nitrogen oxides react with water, oxygen, and other oxidants in the atmosphere, they form acidic compounds that contribute to acid rain. This phenomenon can cause acidification of lakes and streams, potentially harming aquatic life, and it can damage trees and buildings.

Both nitrogen dioxide and sulfur dioxide are considered criteria pollutants by the U.S. Environmental Protection Agency (EPA). This means that their concentrations in the ambient air are useful as indicators of overall air quality and have been established based on health-related criteria and data. These pollutants can cause adverse health effects, including respiratory issues and, in the case of long-term exposure to particulate matter associated with these pollutants, cardiovascular issues and lung cancer.

It is important to recognize that while nitrogen dioxide and sulfur dioxide are significant human-made air pollutants, they are not the only ones. Other human-made pollutants include carbon monoxide, lead, ozone, particulate matter, carbon dioxide, nitrous oxide, methane, chlorofluorocarbons (CFCs), and volatile organic compounds (VOCs). These pollutants, when released into the atmosphere, can have detrimental effects on human health, the environment, and the climate.

Volatile organic compounds (VOCs) are key to the formation of ozone

Volatile organic compounds (VOCs) are organic chemical compounds that can evaporate under normal indoor atmospheric conditions of temperature and pressure. They are emitted as gases from certain solids or liquids and include a variety of chemicals, some of which may have adverse health and environmental effects. VOCs are found in a wide variety of products, such as solvent-based paints, printing inks, consumer products, organic solvents, and petroleum products. They are also emitted by motor vehicles and vessels.

VOCs are key to the formation of ozone. Ozone is a gas composed of three oxygen atoms and occurs both in the Earth's upper atmosphere and at ground level. Stratospheric ozone is considered "good" because it protects living things from ultraviolet radiation from the sun. In contrast, ground-level ozone is considered "bad" as it can trigger health problems, especially for children, the elderly, and people with lung diseases such as asthma.

The formation of ground-level ozone occurs through complex chemical reactions between nitrogen dioxide and VOCs. Under sunlight, VOCs react with nitrogen oxides emitted primarily from vehicles, power plants, and industrial activities. This reaction results in the formation of ozone, which contributes to the creation of fine particulates. The accumulation of ozone, fine particulates, and other gaseous pollutants leads to smog, which reduces visibility and negatively impacts air quality.

To mitigate the impact of VOCs on ozone formation, it is recommended to avoid using VOC-containing products, such as organic cleaning solvents, and to store these products in airtight containers when necessary. Additionally, reducing vehicle usage, sharing rides, and utilizing public transportation can help decrease the emission of VOCs and nitrogen oxides, thereby reducing ozone formation.

While VOCs are a significant contributor to ozone formation, it is important to note that other pollutants, such as nitrogen dioxide, sulfur dioxide, and carbon monoxide, also play a role in air pollution and its associated health and environmental consequences.

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